The invention relates to a display unit in which the activation or driver electronics are disposed on the rear side of a display element.
Flat displays based on LED or LCD technology are increasingly being used in the area of data processing equipment or communication and entertainment electronics. In the process, LCD (liquid crystal diode) technologies are especially becoming widely accepted, on the basis of their contrast, low necessary current and favorable production costs. A customary LCD display in this case includes a top plate that covers the actual liquid crystal element with the liquid crystals and a bottom plate on which the liquid crystal element with the actual liquid crystals is mounted. This sandwich method achieves good protection for the sensitive liquid crystals.
For the electrical activation of the individual liquid crystals, the bottom plate is made larger than the actual liquid crystal, to allow contacts for leading away signal lines to be attached to it. It is customary to use what is known as a flex circuit, that is to say a flat ribbon cable with numerous individual signal lines, to allow the signals to be led to the bottom plate. The actual activation or driver electronics is/are consequently separate from the display unit.
It has also been proposed to dispose the control electronics directly on the protruding part of the bottom plate or bottom glass sheet. Both configurations, known in the prior art, have the disadvantage, however, that the bottom plate must be significantly larger than the actual display area, to allow the flat ribbon cable or the activation electronics to be fastened on it.
Integration of displays, such as LCD displays, in what are known as chip cards has so far not been possible at all on account of the confined lateral space, but in particular on account of the small thickness of chip cards of only at most 0.84 mm (according to ISO 7816, 10373). However, on account of the growing significance of chip cards and the increasing functionality accommodated on them, it would be advantageous also to provide a display capability on chip cards. This applies in particular when a capability of recharging with data or a monetary value is to be used for the purpose of repeated usability.
In the case of customary displays, moreover, the separation of the actual display area and the control electronics involves additional expenditure and further possible sources of faults. It would therefore be advantageous to have a display unit that is more compact, involves lower expenditure to produce and assemble and could possibly be included in chip cards.
It is accordingly an object of the invention to provide a display unit and a method for manufacturing a display unit that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a display unit for chip cards. The display unit includes a display element having a front side, a rear side, and a liquid crystal layer for the front side of the display unit. The display unit also includes a control element being electrically connected to the display element and disposed as an integrated circuit on the rear side of the display unit opposite from the front side.
With the objects of the invention in view, there is also provided a method of producing an LCD display element for chip cards. The first step of the method is providing a display element having a liquid crystal layer. The next step is providing a control element. The next step is providing a bottom sheet with a side having conductor tracks and a region extending beyond the liquid crystal layer. The next step is attaching the display element on the side of the bottom sheet. The next step is attaching the control element on the side of the bottom sheet in the region extending beyond the liquid crystal layer. The next step is folding the bottom sheet between the display element and the control element to form an edge on the bottom sheet, a face facing toward the liquid crystal layer, and a face facing away from the liquid crystal layer that holds the control element. The next step is leading the conductor tracks around the edge of the bottom sheet.
In one aspect, the invention is directed at a display unit in which a control element is positioned directly behind a display element.
In a further aspect, the invention is directed at a display unit of which the base area corresponds substantially to the base area of the liquid crystal.
In another aspect, the invention is directed at a display unit in which it has been possible for fault-prone plug-in connections largely to be minimized.
Accordingly, the invention is directed at a display unit with a front region with at least one display element, a rear region facing away from the front region, with at least one control element for the activation of the at least one display element and electrical lines for the connection of the at least one display element to the at least one control element.
A control element is to be understood here as meaning any electronic device that is capable of making the respectively used display elements display informational contents. For example, the control element may have a driver circuit or a number of circuits that convert the signals coming from an information-representing device into electric currents suitable for the display element.
The control element may in this case be disposed directly on the rear region or be encapsulated by a package. The package improves the control element stability with respect to external influences. A display element for the purposes of the present invention is understood here as meaning any substantially flat element that is suitable for the display of information, for example multi-element LED display modules, multi-element LCD display modules, which are suitable for the representation of numeric or alphanumeric information, matrix-based LED, LCD or plasma screens, mechanically displaying elements, etc. In this case, one or a number of the display elements respectively used may actually be used, for example a number of LED modules, which are respectively suitable for the display of a figure or a letter.
It is particularly preferred for the display element to have an LCD display. A display element that includes different types of individual elements is also conceivable.
When an LCD display is used, it is preferred for it to have a top layer, a liquid crystal layer, a bottom sheet, and for at least one control element to be disposed on the bottom sheet. The configuration of the control element on the bottom sheet may take place by techniques familiar to a person skilled in the art, for example by adhesive attachment, solder, fixing by common frame, etc. The top layer may, in the way already customary in the case of today""s LCD displays, include glass. It may, however, also include a plastic sheet to reduce the thickness of the LCD display and increase the mechanical flexibility, as is necessary for example for use in chip cards. To avoid the absorption of moisture, the plastic sheet may be additionally provided with at least one water-vapor barrier layer.
Also, when other display elements are used as an LCD display, it is preferred for the control element to be disposed directly on the rear side of the at least one display element. In this case, the display element also may have a bottom sheet or bottom plate, which forms its rear side, it then being possible for the control element to be fastened to the bottom sheet or to the bottom plate.
The control element may have a package with a socket. The socket may be connected directly to the bottom sheet or bottom plate. In the case of driver circuits, which have a higher power demand, and as a result greater heat dissipation, this configuration improves cooling. Moreover, it is possible to comply exactly with specifications with respect to the desired depth of a display unit by using socket adapters. When included in chip cards, a socket would increase the thickness of the unit, possibly making it impossible for it to be included. Socketed packages are therefore not preferred when the display units according to the invention are used in chip cards.
The use of packages and sockets is prevented when the displays according to the invention are used in chip cards, because the latter are too thin to be able to accommodate control elements with packages. Therefore, it is preferred as an alternative for the control element to be an integrated circuit without a package, which is connected directly to the bottom sheet or bottom plate. The mounting of the integrated circuit usually takes place by conductive adhesion. Before the integrated circuit is mounted onto the bottom sheet or bottom plate, the integrated circuit forming the control element is thinned on its underside, to fit into a chip card, preferably to a thickness in the range of 0.1 mm to 0.2 mm.
The different improvements including a top sheet of plastic, a thin bottom sheet, and a thinned-back integrated circuit allow a thickness of the display unit of 0.55 mm in the region of the integrated circuit and 0.45 mm in other regions of a correspondingly constructed LCD display to be achieved.
In a particularly preferred embodiment of the present invention, the bottom sheet may be made larger in one dimension than the front region, that region of the bottom sheet that is larger than the front region may be folded back on itself, and the integrated circuit without a package may be connected to the folded-back region of the bottom sheet. To one side, the bottom sheet is consequently larger than it necessarily should be, to accommodate the display element. The bottom sheet is consequently constructed such that it can accommodate both the display elements and the integrated circuit and is flexible enough to be folded back. The folding back may take place directly onto the bottom sheet itself, so that the rear side of the bottom sheet is in contact with itself, but it may also be performed around a further supporting layer, the bottom sheet then having to be led around the edge of the supporting layer.
This configuration allows a particularly thin construction to be produced in a simple way, since, for example, conductor tracks only have to be provided on one side of the bottom sheet to allow the display element(s) and the integrated circuit to be electrically bonded simultaneously. A further advantage of this invention is that one side of the bottom film may be specifically constructed for the attachment of the components, while the other side has, for example, adhesive properties.
In a further preferred embodiment of the invention, the display element and the at least one control element are disposed on the opposite surfaces of a substantially planar supporting structure. Such a supporting structure is appropriate in particular whenever a number of display elements not initially connected to one another are to be used, or the rear side of the display element used is not very suitable in respect of its surface structure for allowing a connection to the at least one control element. The supporting structure consequently represents a common base on which both the display element and the control element can be optimally disposed. In most cases, such a supporting structure will favorably be a printed circuit board, preferably a flexible printed circuit board that can serve at the same time for the electrical signal transmission.
Electrical connection of the at least one display element and the at least one control element by way of the electrical lines may be performed in a variety of ways. For instance, the electrical lines may be led directly through the supporting structure.
Alternatively or simultaneously, the electrical lines may also be led around the edge of the supporting structure of the bottom plate or bottom sheet.
The bottom sheet may preferably be made larger in one dimension than the front region, that region of the bottom sheet that is larger than the front region may be folded back on itself, and the electrical lines may connect the front region of the bottom sheet to the folded-back region of the bottom sheet. This configuration is preferably combined with that described above, in which an integrated circuit is applied directly to the folded-back region of the bottom sheet.
If a surface suitable for the purpose, for example a folded-back bottom sheet, is available, the electrical lines may be led out as conductor tracks. This is appropriate in particular when a folded-back bottom sheet is used.
The electrical lines may likewise be configured as a flexible flat ribbon or as foil conductors, for example in the form of an inlay sheet.
The various types of electrical lines that can be used according to the invention can be combined with one another as desired, according to the electrical or spatial requirements, to allow optimum routing of the electrical lines to be achieved.
Specifically, when LCD display units are used, it is necessary to lead the electrical lines around the bottom sheet or bottom plate, since leading through the bottom plate, as is possible in the case of conventional printed circuit boards, is not possible here.
In some applications, for example again in the case of chip cards, it may cause thermal problems if heat is required when the integrated circuit is mounted or if the heat-producing integrated circuit is disposed directly behind the display elements, in particular in the case of the typically sensitive LCD displays. Therefore, in such cases, the integrated circuit is preferably disposed at a distance from the actual display element(s). This can be achieved by the control element being disposed in a region of the rear region of which the front region has no display element disposed on it. For example, it is possible to form on one side of the display unit, for example in the bottom plate or bottom sheet, an overhang, to the rear side of which the control element can be attached.
In an alternative embodiment, the electrical lines may also be direct connections between outputs of the at least one display element and outputs of the at least one control element. In the case of this particularly simple embodiment of the invention, the outputs of the various elements involved, that is to say the display elements and the control elements, are constructed in such a way that, when their two undersides are placed one on top of the other, they are directly opposed with their electrical outputs. This allows the outputs to be directly connected by way of electrical soldered joints. Consequently, in the case of this embodiment, no continuing conductor tracks or other electrical lines are necessary.
The display unit according to the invention may, furthermore, have a signal line bus for the connection of the at least one control element to a device that can or does display information on the display unit. Such a signal line bus is only used, however, for the transmission of the actual information signals, but not for the transmission of direct control lines for activating the individual segments of a display element. Consequently, considerably fewer lines are required than in the prior art.
The invention is finally also directed at the use of a display unit according to the invention for inclusion in compact devices, in which the lateral dimensions in the direction of the plane of the display are to correspond substantially to the size of the display unit.
The use may be characterized in that the inclusion takes place in chip cards. Suitable for performing inclusion is a cold adhering technique with cyanoacrylate. Cold adhering techniques with cyanoacrylate improves topography, does not subject the rear wall of the card to thermomechanical stresses, and also cannot cause thermally induced damage in the display unit.
The configuration according to the invention of the individual elements of the display unit leads to devices that are much more compact in plan view than was possible in the case of prior-art devices.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a display unit and a method for manufacturing a display unit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.